JP4819122B2 - Liquid crystal display device and viewing angle control panel - Google Patents

Description

  The present invention relates to a viewing angle control panel that switches a viewing angle of a display panel between a wide viewing angle and a narrow viewing angle, and a liquid crystal display device including the viewing angle control panel.

  In general, a display device is required to have a viewing angle as wide as possible so that a clear image can be seen from any viewing angle. In particular, liquid crystal display devices that have been widely used recently have been developed for various viewing angles because the liquid crystal itself has a viewing angle dependency.

  However, depending on the usage environment, it may be more convenient for the viewing angle to be narrow so that only the user himself can view the display content. In particular, a notebook personal computer, a portable information terminal (PDA: Personal Data Assistant), a mobile phone, or the like is highly likely to be used in a place where an unspecified number of people can exist, such as in a train or an airplane. In such a use environment, it is desirable that the viewing angle of the display device is narrow because it is not desirable to look into the display contents from other people in the vicinity from the viewpoint of maintaining confidentiality and protecting privacy. Thus, in recent years, there is an increasing demand for switching the viewing angle of a single display device between a wide viewing angle and a narrow viewing angle depending on the usage situation. This requirement is not limited to the liquid crystal display device, but is a common problem for any display device.

  In response to such a request, for example, Patent Document 1 includes a phase difference control device in addition to a display device that displays an image, and controls the voltage applied to the phase difference control device to control the viewing angle characteristics. Techniques to change are proposed. Patent Document 1 exemplifies chiral nematic liquid crystal, homogeneous liquid crystal, random alignment nematic liquid crystal, and the like as the liquid crystal mode used in the liquid crystal display device for phase difference control.

  Further, for example, in Patent Document 2 and Patent Document 3, a viewing angle control liquid crystal panel is provided on the upper part of the display liquid crystal panel, and these panels are sandwiched between two polarizing plates, and are attached to the viewing angle control liquid crystal panel. A configuration in which viewing angle control is performed by adjusting an applied voltage is also disclosed. In Patent Document 2, the liquid crystal mode of the viewing angle control liquid crystal panel is a twisted nematic system.

Further, for example, in Patent Document 4, a first state in which a first viewing angle range is provided between a backlight and a display device, and a second viewing angle range that is narrower than the first viewing angle range. A display having a liquid crystal device that is switchable between a second state of providing a display and a second state is disclosed.
Japanese Patent Publication “Japanese Patent Laid-Open No. 11-174489 (published July 2, 1999)” Japanese Patent Publication “Japanese Patent Laid-Open No. 10-268251 (published on Oct. 9, 1998)” Japanese Patent Publication “Japanese Patent Laid-Open No. 2005-309020 (published Nov. 4, 2005)” Japanese Patent Publication “JP 2005-316470 A” (published on November 10, 2005) “Nitto Denko Technical Report” 84 (Vol.41), 26-29, 2003

  However, in the above-mentioned conventional patent document 1, it is stated that switching between a wide viewing angle and a narrow viewing angle is possible by using a liquid crystal device for phase difference control, but the effect is not sufficient. For example, Patent Document 1 shows an isocontrast curve having a contrast ratio of 10: 1 as shown in FIG. 16, and the contrast in the wide viewing angle direction is certainly lowered in the narrow viewing angle mode. However, with such a change, the display is sufficiently visually recognized by the person next to it.

  In general, even if the contrast ratio is reduced to 2: 1, the display can be sufficiently visually recognized.

  The techniques of Patent Documents 2 to 4 also switch the wide viewing angle and the narrow viewing angle by adjusting the contrast by changing the voltage applied to the viewing angle control liquid crystal panel. The effect is not enough.

  That is, any technique of Patent Documents 1 to 4 adopts a method of switching between a wide viewing angle and a narrow viewing angle by reducing the contrast in the wide viewing angle direction. This method has a problem that there is a possibility that an image may be seen from others because the shielding in the wide viewing angle direction is not sufficient when the viewing angle is narrow.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a viewing angle control panel capable of increasing a shielding effect and a liquid crystal display device including the same.

  In order to solve the above problems, a liquid crystal display device according to the present invention has a backlight, a liquid crystal display panel, a viewing angle of the liquid crystal display panel, a first viewing angle, and a first viewing angle within the first viewing angle. And a viewing angle control panel that switches between a second viewing angle that is narrower than the first viewing angle, the viewing angle control panel comprising: a first polarizing plate; a liquid crystal layer; Two polarizing plates are stacked in this order, and at least one of the first polarizing plate and the liquid crystal layer and at least one of the second polarizing plate and the liquid crystal layer The retardation value Re1 of the white display portion when at least one retardation plate is provided and the viewing angle of the liquid crystal display panel is the first viewing angle is nλ / 2−λ / 4 <Re1. <Nλ / 2 + λ / 4 (n is an integer of 1 or more), and the liquid The retardation value Re2 of the white display portion when the viewing angle of the display panel is the second viewing angle is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4 (n is an integer of 1 or more), The retardation value Re3 of the black display portion when the viewing angle of the liquid crystal display panel is the second viewing angle is nλ−λ / 4 <Re3 <nλ + λ / 4 (n is an integer of 1 or more). And

  According to the above configuration, when the second viewing angle is narrower than the conventional viewing angle control panel, the shielding region is expanded as compared with the conventional viewing angle control panel (that is, the visible viewing angle range is narrower). A liquid crystal display device can be provided. Therefore, a liquid crystal display device that cannot be visually recognized from directions other than a specific direction and has excellent performance in terms of privacy protection and security improvement can be provided.

  Here, the “white display portion” means an area where light can be transmitted and the display can be visually recognized, and the “black display portion” means an area where light is shielded and the display cannot be visually recognized. Therefore, the “white display portion” can be rephrased as a “viewing region” and the “black display portion” can be restated as a “non-viewing region”. Here, the retardation value is a phase shift between each component of light that has passed through the viewing angle control panel (more specifically, the phase of light traveling in the plane including the slow axis and the fast axis). The phase of light traveling in the plane including

  In the liquid crystal display device of the present invention, the retardation value Re1 is nλ / 2 (n is an integer of 1 or more), the retardation value Re2 is nλ / 2 (n is an integer of 1 or more), and the retardation value Re3 is nλ (n is an integer of 1 or more) is preferable. According to the above configuration, the viewing angle can be further narrowed in the second viewing angle.

  In addition to the above configuration, the liquid crystal display device of the present invention has a polar angle Φ that is an angle between a straight line connecting the center of the surface of the viewing angle control panel and the viewpoint and a normal line at the center of the surface of the viewing angle control panel. An arbitrary viewpoint satisfying Φ = 45 ° is set as the first viewpoint, and a leg of a perpendicular line dropped from the first viewpoint to a plane including the surface of the viewing angle control panel, and a center of the surface of the viewing angle control panel, Is the azimuth angle θ, the viewpoint with θ = 90 ° and Φ = 45 ° is the second viewpoint, and the viewpoint with θ = 180 ° and Φ = 45 ° is the third viewpoint. If the viewpoint from θ = 270 ° and Φ = 45 ° is the fourth viewpoint, and the viewpoint from the Φ = 0 ° direction is the fifth viewpoint, the first viewing angle is the first viewing angle at the second viewing angle. The retardation value at the viewpoint and the fifth viewpoint is nλ / 2−λ / 4 to nλ / 2 + λ / 4 (n is an integer of 1 or more) Next, the second viewpoint, the third viewpoint, and (the n 1 or more integer) the retardation value is nλ-λ / 4~nλ + λ / 4 in the fourth aspect may become preferable.

  According to the above configuration, at the second viewing angle, the display can be visually recognized only in the two viewpoints of the first viewpoint and the fifth viewpoint among the above five viewpoints, and the other three The display cannot be visually recognized from the viewpoint. Therefore, visual recognition from the vicinity of the second to fourth viewpoints can be reliably prevented.

  In addition to the above configuration, the liquid crystal display device of the present invention includes the retardation plate between the first polarizing plate and the liquid crystal layer, and between the second polarizing plate and the liquid crystal layer. Are preferably provided.

  According to the above configuration, the left and right directions and the downward direction of the display panel (the azimuth angle θ shown in FIG. 3 is in the range of 90 ° to 270 °) can be displayed in black at the second viewing angle. Visual recognition from these directions can be prevented more reliably.

  In addition to the above-described configuration, the liquid crystal display device of the present invention includes at least one of the above-described configuration between the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer. It is preferable that a plurality of phase difference plates are provided so that the refractive indexes of the phase difference plates stacked on each other are different from each other.

  According to said structure, the viewing angle control panel which has the above retardation values can be easily comprised using the existing phase difference plate.

  In the liquid crystal display device of the present invention, in addition to the above-described configuration, the retardation plate includes a λ / 4 plate, a negative C plate, and three main refractive indexes nx, ny in the x, y, and z axis directions orthogonal to each other. , Nx, nx> nz> ny, and a biaxial phase difference plate having a relationship of (nx−nz) /|nx−ny|=0.1. preferable.

The negative C plate has a relationship of nx = ny> nz when having three main refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other.
According to said structure, the phase difference plate which has the above retardation values can be comprised more reliably.

  In addition to the above-described configuration, the liquid crystal display device of the present invention includes at least one of the above-described configuration between the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer. It is preferable that at least a λ / 4 plate and a negative C plate are provided as the phase difference plate.

  According to said structure, the phase difference plate which has the above retardation values can be obtained, and a more favorable narrow viewing angle characteristic can be obtained.

  In addition to the above configuration, the liquid crystal display device of the present invention includes a negative C plate, a λ / 4 plate, and the biaxial retardation plate as the retardation plate, and includes the first polarizing plate, the liquid crystal layer, and the like. And at least one of the second polarizing plate and the liquid crystal layer includes a negative C plate, a λ / 4 plate, and the biaxial retardation plate in this order from the side adjacent to the liquid crystal layer. It is preferable that they are laminated.

  According to said structure, the phase difference plate which has the above retardation values can be obtained, and a more favorable narrow viewing angle characteristic can be obtained.

  In the liquid crystal display device of the present invention, in addition to the above configuration, the polarization transmission axes of the first polarizing plate and the second polarizing plate constituting the viewing angle control panel are preferably orthogonal to each other. In other words, in the viewing angle control panel, it is preferable that the polarization transmission axes of the two polarizing plates arranged opposite to each other with the liquid crystal layer interposed therebetween are arranged to be orthogonal to each other. Here, each polarization transmission axis being orthogonal to each other is used to mean that each polarization transmission axis is substantially orthogonal to each other. Here, the polarization transmission axes being substantially orthogonal to each other means that the range of angles formed by the polarization transmission axes is 80 ° to 100 °.

  According to said structure, the viewing angle switch which has a sufficient difference in a viewing angle range between a 1st viewing angle and a 2nd viewing angle can be performed.

  In order to solve the above problems, a viewing angle control panel according to the present invention is disposed on at least one of the back surface and the front surface of a display device that displays an image, and the viewing angle of the display device is defined as a first viewing angle. A viewing angle control panel that switches between a second viewing angle within the first viewing angle and narrower than the first viewing angle, the first polarizing plate, the liquid crystal layer, and the second polarizing plate Are stacked in this order, and at least one between the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer is a retardation plate. Is provided, and the retardation value Re1 of the white display portion when the viewing angle of the display device is the first viewing angle is nλ / 2−λ / 4 <Re1 <nλ / 2 + λ / 4 (n is an integer of 1 or more), and the viewing angle of the display device is the first number. The retardation value Re2 of the white display portion when the viewing angle is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4 (n is an integer of 1 or more), and the viewing angle of the display device is the first viewing angle. The retardation value Re3 of the black display portion when the viewing angle is 2 is nλ−λ / 4 <Re3 <nλ + λ / 4 (n is an integer of 1 or more).

  According to the above configuration, at the second viewing angle with a narrower viewing angle, the shielding region is expanded more than the conventional viewing angle control panel (that is, the visible viewing angle range is narrower). )be able to. Therefore, by disposing the viewing angle control panel of the present invention on at least one of the back surface and the front surface of the display device, the viewing angle control panel is not visible from a direction other than a specific direction, and is excellent in terms of privacy protection and security enhancement. A display device having performance can be provided.

  Here, the “white display portion” means an area where light can be transmitted and the display can be visually recognized, and the “black display portion” means an area where light is shielded and the display cannot be visually recognized. Therefore, the “white display portion” can be rephrased as a “viewing region” and the “black display portion” can be restated as a “non-viewing region”. Here, the retardation value is a phase shift between each component of light that has passed through the viewing angle control panel (more specifically, the phase of light traveling in the plane including the slow axis and the fast axis). The phase of light traveling in the plane including

  In the viewing angle control panel according to the present invention, the retardation value Re1 is nλ / 2 (n is an integer of 1 or more), the retardation value Re2 is nλ / 2 (n is an integer of 1 or more), and the retardation value Re3 is nλ (n is an integer of 1 or more) is preferable.

  According to the above configuration, the viewing angle can be further narrowed in the second viewing angle.

  In addition to the above-described configuration, the viewing angle control panel of the present invention has a polar angle Φ that is an angle between a straight line connecting the center of the surface of the viewing angle control panel and the viewpoint and a normal line at the center of the surface of the viewing angle control panel. An arbitrary viewpoint satisfying Φ = 45 ° is set as the first viewpoint, and a leg of a perpendicular line dropped from the first viewpoint to a plane including the surface of the viewing angle control panel and the center of the surface of the viewing angle control panel. Is the azimuth angle θ, the viewpoint with θ = 90 ° and Φ = 45 ° is the second viewpoint, and the viewpoint with θ = 180 ° and Φ = 45 ° is the third viewpoint. Assuming that the viewpoint is θ = 270 ° and Φ = 45 ° is the fourth viewpoint, and the viewpoint from the Φ = 0 ° direction is the fifth viewpoint, the first viewing angle is the first viewing angle at the second viewing angle. And the retardation value at the fifth viewpoint is nλ / 2−λ / 4 to nλ / 2 + λ / 4 (where n is 1 or more). Number), and the second viewpoint, the third viewpoint, and the retardation value is nλ-λ / 4~nλ + λ / 4 (n in the above fourth aspect may become an integer of 1 or more) preferred.

  According to the above configuration, at the second viewing angle, the display can be visually recognized only in the two viewpoints of the first viewpoint and the fifth viewpoint among the above five viewpoints, and the other three The display cannot be visually recognized from the viewpoint. Therefore, visual recognition from the vicinity of the second to fourth viewpoints can be reliably prevented.

  Other objects, features, and advantages of the present invention will be fully understood from the following description. The benefits of the present invention will become apparent from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a liquid crystal display device according to an embodiment of the present invention, and is a cross-sectional view illustrating a configuration of a liquid crystal display device including a viewing angle control panel. FIG. 2 is a perspective view showing an arrangement state of liquid crystal molecules at a narrow viewing angle of the viewing angle control panel of FIG. 1. FIG. 2 is a perspective view showing an arrangement state of liquid crystal molecules when the viewing angle control panel of FIG. 1 is at a wide viewing angle. FIG. 3 is a schematic diagram illustrating definition of a viewing angle and explaining each viewpoint with respect to a viewing angle control panel arranged in the same direction as in FIGS. 2A and 2B. It is a figure which shows the positional relationship of the liquid crystal molecule according to a viewing angle, and the polarization transmission axis of a polarizing plate. It is a figure which shows the positional relationship of the liquid crystal molecule according to a viewing angle, and the polarization transmission axis of a polarizing plate. It is a figure which shows the positional relationship of the liquid crystal molecule according to a viewing angle, and the polarization transmission axis of a polarizing plate. It is a chart which shows the luminance distribution at the time of a narrow viewing angle of a liquid crystal display device when the retardation plate is not provided in the viewing angle control panel. It is a chart which shows the luminance distribution at the time of the wide viewing angle of a liquid crystal display device when the retardation plate is not provided in the viewing angle control panel. It is a schematic diagram which shows a structure in case a viewing angle control panel has one phase difference plate. 8 shows a refractive index ellipsoid of liquid crystal molecules of the viewing angle control panel shown in FIG. The refractive index ellipsoid of the phase difference plate provided in the viewing angle control panel shown in FIG. As a comparative example, it is a schematic diagram showing a refractive index ellipsoid of a retardation plate conventionally used for widening the viewing angle of a liquid crystal display device. In the viewing angle control panel shown in FIG. 7, it is a schematic diagram showing the relationship between the polarization transmission axis, the refractive index ellipsoid of the liquid crystal molecules, and the refractive index ellipsoid of the phase difference plate, and the viewing angle from around 90 ° azimuth. It is. In the viewing angle control panel shown in FIG. 7, it is a schematic diagram showing the relationship between the polarization transmission axis, the refractive index ellipsoid of the liquid crystal molecules, and the refractive index ellipsoid of the phase difference plate, and the viewing angle from around 0 ° azimuth. It is. It is sectional drawing which shows the structure of the viewing angle control panel of the liquid crystal display device shown in FIG. The schematic diagram of a phase difference plate is shown. The refractive index ellipsoid of the NEZ plate which comprises the phase difference plate of a viewing angle control panel is shown. The refractive index ellipsoid of (lambda) / 4 board which comprises the phase difference plate of a viewing angle control panel is shown. The refractive index ellipsoid of the negative C plate which comprises the phase difference plate of a viewing angle control panel is shown. FIG. 3 is a schematic diagram illustrating definition of a viewing angle and explaining each viewpoint with respect to a viewing angle control panel arranged in the same direction as in FIGS. 2A and 2B. 11 is a chart showing a luminance distribution at a narrow viewing angle of a liquid crystal display device provided with the viewing angle control panel shown in FIG. 10. 11 is a chart showing a luminance distribution at a wide viewing angle of a liquid crystal display device provided with the viewing angle control panel shown in FIG. It is sectional drawing which shows the other structural example of the viewing angle control panel of the liquid crystal display device shown in FIG. It is sectional drawing which shows the other structural example of the viewing angle control panel of the liquid crystal display device shown in FIG. It is sectional drawing which shows the other structural example of the viewing angle control panel of the liquid crystal display device shown in FIG. FIG. 9 is a cross-sectional view illustrating a modification of the liquid crystal display device illustrated in FIG. 1 and illustrating a configuration of the liquid crystal display device including a display liquid crystal panel on the upper side of the viewing angle control panel. It is a chart which shows the viewing angle distribution of the liquid crystal display device provided with the conventional viewing angle control panel.

Explanation of symbols

1. LCD panel for display (LCD panel)
2 Viewing Angle Control Panel 2a Viewing Angle Control Panel 2b Viewing Angle Control Panel 2c Viewing Angle Control Panel 3 Backlight 10 Liquid Crystal Display Device 10a Liquid Crystal Display Device 11 Liquid Crystal Cell 12 Liquid Crystal Panel Upper Polarizer 13 Liquid Crystal Panel Lower Polarizer 21 Liquid Crystal Cell ( Liquid crystal layer)
22 Polarizing plate on control panel (first polarizing plate)
23 Control panel lower polarizing plate (second polarizing plate)
24 Upper retardation plate (retardation plate)
25 Lower retardation plate (retardation plate)
31a NEZ (retardation plate)
31b NEZ (retardation plate)
32a λ / 4 plate (retardation plate)
32b λ / 4 plate (retardation plate)
33a Negative C plate (retardation plate)
33b Negative C plate (retardation plate)
X ₂₂ polarization transmission axis X ₂₃ polarization transmission axis

  An embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.

  In addition, each figure referred below demonstrates only the main member required in order to demonstrate this invention among the structural members of one Embodiment of this invention, simplifying and showing for convenience of explanation. Therefore, the liquid crystal display device of the present invention can include arbitrary constituent members not shown in the drawings referred to in this specification. Moreover, the dimension of the member in each figure does not represent the dimension of an actual structural member, the dimension ratio of each member, etc. faithfully.

  First, the structure of the liquid crystal display device 10 of this Embodiment is demonstrated based on FIG. FIG. 1 is a cross-sectional view showing a schematic configuration of the liquid crystal display device 10.

  As shown in FIG. 1, a liquid crystal display device 10 includes two liquid crystal panels, a display liquid crystal panel 1 (liquid crystal display panel) as a display panel for displaying an image and a viewing angle control panel 2 including a liquid crystal cell 21. It has. The display liquid crystal panel 1 is a transmissive type, and a backlight 3 is used as a light source.

  The viewing angle control panel 2 is provided, for example, between the backlight 3 and the display liquid crystal panel 1 as shown in FIG.

  The liquid crystal display device 10 performs a switching operation of the liquid crystal in the viewing angle control panel 2 to thereby display a wide viewing angle (first viewing angle) in which the viewing angle at which an image on the display liquid crystal panel 1 can be viewed is wide, and a display It is possible to switch the display mode in two modes: a narrow viewing angle (second viewing angle), which is a state where the viewing angle at which an image of the liquid crystal panel 1 can be viewed is narrow. The narrow viewing angle is particularly preferably used when it is not desired for others to view the image on the display liquid crystal panel 1, and the wide viewing angle is used for other normal use or a plurality of images on the display liquid crystal panel 1. It is preferably used when a person wants to watch at the same time.

  The display liquid crystal panel 1 includes a liquid crystal cell 11 having a liquid crystal sandwiched between a pair of translucent substrates, a liquid crystal panel upper polarizing plate 12 and a liquid crystal panel lower polarizing plate 13 provided on the front and back of the liquid crystal cell 11. ing. The liquid crystal mode and the cell structure of the liquid crystal cell 11 are arbitrary. Further, the drive mode of the display liquid crystal panel 1 is also arbitrary. That is, as the display liquid crystal panel 1, any liquid crystal panel capable of displaying characters, images, or moving images can be used. Therefore, in FIG. 1, the detailed structure of the display liquid crystal panel 1 is not shown, and the description thereof is also omitted.

  The display liquid crystal panel 1 may be a panel capable of color display or a panel dedicated to monochrome display. Further, the configuration of the backlight 3 is not limited at all, and any known backlight can be used. Therefore, illustration and description of the detailed structure of the backlight 3 are also omitted.

  2A and 2B, the viewing angle control panel 2 includes a liquid crystal cell 21 (liquid crystal layer) in which a liquid crystal layer is sandwiched between a pair of light-transmitting substrates 21a and 21b described later. And two retardation plates (an upper retardation plate 24 and a lower retardation plate 25) disposed with the liquid crystal cell 21 interposed therebetween, and an upper portion of the upper retardation plate 24, that is, on the display liquid crystal panel 1 side of the liquid crystal cell 21. The control panel upper polarizing plate 22 (first polarizing plate) and the control panel lower polarizing plate 23 (second polarizing plate) provided below the lower retardation plate 25, that is, on the backlight 3 side of the liquid crystal cell 21. ). The liquid crystal layer of the liquid crystal cell 21 is composed of homogeneously aligned positive nematic liquid crystal.

  In other words, the viewing angle control panel 2 has a configuration in which the control panel lower polarizing plate 23, the liquid crystal cell 21, and the control panel upper polarizing plate 22 are arranged in this order, and the control panel lower polarizing plate 23 and the liquid crystal cell. A lower retardation plate 25 is provided between the liquid crystal cell 21 and the upper polarizing plate 22 on the control panel.

  The control panel upper polarizing plate 22 has a surface subjected to diffusion treatment such as AG treatment. The lower polarizing plate 23 of the control panel is a so-called clear polarizing plate that is not subjected to surface treatment. The polarizing plate 22 on the control panel is not always necessary and can be omitted. That is, it is sufficient that at least one polarizing plate exists between the viewing angle control panel 2 and the display liquid crystal panel 1, so that the liquid crystal panel lower polarizing plate 13 of the display liquid crystal panel 1 is used as the control panel upper polarizing plate 22. It is possible to share it. In this case, the liquid crystal panel lower polarizing plate 13 corresponds to the polarizing plate of the present invention.

  Next, the configuration and operation of the viewing angle control panel 2 will be described with reference to FIGS. 2 (a) and 2 (b). For convenience of explanation, here, a configuration in which the viewing angle control panel 2 is not provided with a retardation plate will be described first, and a more detailed description of the retardation plate provided in the viewing angle control panel according to the present embodiment will be given. The structure will be described later.

  2 (a) and 2 (b) are schematic diagrams mainly showing the configuration of the viewing angle control panel 2, and FIG. 2 (a) shows an arrangement state of liquid crystal molecules at a narrow viewing angle, and FIG. b) shows the alignment state of the liquid crystal molecules at a wide viewing angle.

  As shown in FIGS. 2A and 2B, the liquid crystal cell 21 of the viewing angle control panel 2 includes a pair of translucent substrates 21a and 21b. Transparent electrodes (not shown) are formed on the surfaces of the translucent substrates 21a and 21b using, for example, ITO (Indium Tin Oxide). The display liquid crystal panel 1 has an electrode structure corresponding to the display unit because it is necessary to drive the liquid crystal in a display unit such as a pixel unit or a segment unit. However, the viewing angle control panel 2 is not limited regarding the electrode structure. For example, a uniform transparent electrode may be formed on the entire surface of the translucent substrates 21a and 21b in order to perform uniform switching over the entire display surface, or any other electrode structure may be employed.

  An alignment film (not shown) for aligning the liquid crystal molecules 21c is formed on the upper layer of the transparent electrode. The alignment film is rubbed by a known method. In FIG. 2A and FIG. 2B, the rubbing directions in each of the translucent substrates 21a and 21b are indicated by arrows Ra and Rb. As shown in FIGS. 2A and 2B, the rubbing direction Ra with respect to the alignment film of the translucent substrate 21a is parallel and opposite to the rubbing direction Rb with respect to the alignment film of the translucent substrate 21b.

  In other words, the liquid crystal cell 21 is a so-called parallel cell having a twist angle of 0 (no twist). In the present embodiment, the liquid crystal injected into the liquid crystal cell 21 is a homogeneously aligned liquid crystal. Therefore, the liquid crystal molecules 21c of the liquid crystal cell 21 are arranged so that the molecular long axes are parallel to the substrate surfaces of the translucent substrates 21a and 21b when no voltage is applied. The retardation value d · Δn (d is the thickness of the cell, Δn is the birefringence) of the liquid crystal cell 21 is, for example, 350 nm to 450 nm.

In addition, when a voltage is applied between electrodes (not shown) provided on each of the translucent substrates 21a and 21b, the liquid crystal molecules 21c are in a transparent state as shown in FIG. The direction is gradually changed according to the magnitude of the applied voltage in a plane perpendicular to the normal lines of the light-transmitting substrates 21a and 21b and parallel to the rubbing directions Ra and Rb with respect to the alignment film of the light-transmitting substrate 21a. When the applied voltage reaches a predetermined value, the liquid crystal molecules 21c are arranged in a state in which the molecular major axis is substantially perpendicular to the substrate surfaces of the translucent substrates 21a and 21b, as shown in FIG. That is, FIG. 2A shows that the molecular long axis of the liquid crystal molecules 21c is in relation to the normal line of the translucent substrates 21a and 21b by the applied voltage V _L (for example, a voltage of about 2.5 V to 3.5 V). Slightly tilted. FIG. 2B shows a state in which the molecular major axis of the liquid crystal molecules 21c is substantially perpendicular to the substrate surfaces of the translucent substrates 21a and 21b by the applied voltage V _H (for example, a voltage of 5.0 V or more). Indicates.

As shown in FIG. 2A, the control panel lower polarizing plate 23 provided below the liquid crystal cell 21 and the control panel upper polarizing plate 22 provided above the liquid crystal cell 21 in the viewing angle control panel 2 are: The respective polarization transmission axes X ₂₃ and the polarization transmission axes X ₂₂ are arranged so as to be substantially orthogonal to each other.

Thus, the polarization transmission axes X ₂₃ and the polarizing transmission axis X ₂₂ is long as it is arranged so as to be substantially perpendicular to each other (i.e., the angle between the polarizing transmission axis X ₂₂ and the polarizing transmission axis X _23, 80 ° ~ If it is in the range of 100 °, a sufficient effect of switching the viewing angle can be obtained. Polarization transmission axis _{X 22} of the control panel upper polarizing plate 22, with respect to the rubbing direction R of the alignment film of the light transmitting substrate 21a, with a slope of 40 ° to 50 ° (preferably 45 °).

Here, in addition to FIGS. 2A and 2B described above, referring to FIGS. 3 and 4A to 4C, the viewing angle control panel 2 having the above-described configuration is used. The principle of switching the viewing angle between a wide viewing angle and a narrow viewing angle will be described. That is, the viewing angle control panel 2 switches the viewing angle between the wide viewing angle and the narrow viewing angle by switching the voltage applied to the liquid crystal cell 21. In the following description, the viewing angle from a certain viewpoint with respect to the viewing angle control panel 2 is represented by an azimuth angle θ and a polar angle Φ with respect to the center of the upper polarizing plate 22 on the control panel. FIG. 3 shows viewing angles from _three viewpoints P _{1 to} P _{3 with} respect to the viewing angle control panel 2 arranged in the same direction as in FIGS. 2 (a) and 2 (b).

As shown in FIG. 3, the azimuth angle θ is a rotation angle of a line connecting a leg of a perpendicular line dropped from a viewpoint to a plane including the surface of the control panel upper polarizing plate 22 and a center 22 c of the control panel upper polarizing plate 22. It is. In Figure 3, the azimuth theta, the azimuth angle of the direction of the viewpoint P ₁ as 0 °, it is assumed to increase in a clockwise direction when viewed from the normal direction upper side of the control panel on the polarizing plate 22. In Figure 3, the azimuth angle theta ₂ of the viewpoint _{P 2} is 90 °, the azimuth angle theta ₃ of the viewpoint _{P 3} is 180 °. The polar angle Φ is an angle formed by a straight line connecting the center 22c of the polarizing plate 22 on the control panel and the viewpoint with the normal line of the polarizing plate 22 on the control panel.

Here, referring to FIGS. 4A to 4C, the molecular major axis of the liquid crystal molecules 21c is translucent as shown in FIG. 2A by the applied voltage _VL to the liquid crystal cell 21. The display state observed from the respective viewing angles of the viewpoints P _{1 to} P ₃ shown in FIG.

First, with respect to the viewing angle (azimuth angle θ ₁ = 0 °) from the viewpoint P ₁ shown in FIG. 3, as shown in FIG. 4A, the short axis side of the liquid crystal molecules 21c is opposed to the viewing angle direction. Become. Thus, for the visual angle from the viewpoint P _1, emitted from the backlight 3, linearly polarized light incident on the liquid crystal cell 21 is transmitted through the control panel under the polarizing plate 23, given a birefringence by the liquid crystal molecules 21c Instead, the light is shielded by the polarizing plate 22 on the control panel. Therefore, the viewing angle from the viewpoint P ₁ (azimuth angle θ ₁ = 0 °) is black. When the applied voltage _VL to the liquid crystal cell 21 is about 2.5 V to 3.5 V as described above, the polar angle Φ is approximately about the polar angle Φ at the position of the azimuth angle θ ₁ = 0 ° as shown in FIG. In the range of 30 ° ≦ Φ <90 °, a light-shielding state sufficient to prevent peeping from others is obtained. Incidentally, in FIG. _5, L 1 ~L ₈ are ^{luminance, 50cd / m 2, 100cd /} m 2, 150cd / m 2, 200cd / m 2, 250cd / m 2, 300cd / m 2, 350cd / m 2 And equipotential lines showing the distribution of viewing angles of 400 cd / m ² .

For the viewing angle (azimuth angle θ ₂ = 90 °) from the viewpoint P ₂ shown in FIG. 3, as shown in FIG. 4B, the molecular major axis of the liquid crystal molecules 21c is the polarizing plate on the control panel. The polarization transmission axis X22 of ₂₂ and the control panel lower polarizing plate 23 are slightly inclined. Thus, for the visual angle from the viewpoint P _2, emitted from the backlight 3, linearly polarized light incident on the liquid crystal cell 21 is transmitted through the control panel under the polarizing plate 23, negligible birefringence by the liquid crystal molecules 21c Although refraction occurs, it is shielded by the upper polarizing plate 22 on the control panel. Accordingly, black is also displayed for the viewing angle from the viewpoint P ₂ (azimuth angle θ ₂ = 90 °). Further, the viewpoint P ₂ position opposite to, that is, by the same principle as when observed from the viewpoint P ₂ may azimuth θ is 270 °, a black display. When the applied voltage _VL to the liquid crystal cell 21 is about 2.5 V to 3.5 V as described above, the azimuth angle θ = 90 ° and the azimuth angle θ = 270 ° are as shown in FIG. In the range of about 30 ° ≦ Φ <90 ° with respect to the angle Φ, a light shielding state sufficient to prevent peeping from others is obtained.

For the viewing angle (azimuth angle θ ₃ = 180 °) from the viewpoint P ₃ shown in FIG. 3, as shown in FIG. 4 (c), the molecular major axis of the liquid crystal molecules 21c is the polarizing plate on the control panel. about 45 ° inclination with respect to 22 each polarization transmission axis X ₂₃ of the polarizing transmission axis X ₂₂ and the control panel under the polarizing plate 23 of, and a state where the long axis side of the liquid crystal molecules 21c faces the visual angle direction. Thereby, for the viewing angle from the viewpoint P ₃ , the linearly polarized light emitted from the backlight 3 and transmitted through the control panel lower polarizing plate 23 and incident into the liquid crystal cell 21 is birefringent by the liquid crystal molecules 21 c. The polarization direction is rotated so as to coincide with the polarization transmission axis X ₂₂ of the control panel upper polarizing plate 22, and the control panel upper polarizing plate 22 is transmitted. Thus, for the visual angle from the viewpoint P _3, excellent display can be obtained. When the applied voltage _VL is about 2.5V to 3.5V as described above, the azimuth angle θ ₃ = 180 ° is approximately 0 ° ≦ Φ <with respect to the polar angle Φ as shown in FIG. Good display can be obtained in the range of 90 °.

As described above, when the applied voltage _VL for tilting the molecular long axis of the liquid crystal molecules 21c by a slight angle with respect to the substrate normal is applied to the liquid crystal cell 21 of the viewing angle control panel 2, the azimuth angle θ is about 180 °. Good display can be obtained only in a narrow viewing angle range, and for other azimuth angles, the polarized light in the liquid crystal cell 21 is shielded by the lower polarizing plate 13 of the liquid crystal panel, resulting in black display. Therefore, by applying the applied voltage _VL to the liquid crystal cell 21 of the viewing angle control panel 2, the emitted light from the backlight 3 can be shielded in the wide viewing angle direction. That is, the display image of the display liquid crystal panel 1 cannot be viewed from the wide viewing angle direction, and the liquid crystal display device 10 can have a narrow viewing angle.

On the other hand, when an applied voltage V _H that tilts the molecular major axis of the liquid crystal molecules 21c substantially perpendicular to the substrate is applied to the liquid crystal cell 21 of the viewing angle control panel 2 as shown in FIG. As shown in FIG. 6, for any viewing angle of the viewpoints P _{1 to} P ₃ shown, sufficient birefringence is generated so that a good display can be obtained with respect to the omnidirectional angle θ. 10 can be a wide viewing angle. In FIG. 6, L _{1 to} L ₈ have luminances of 130 cd / m ² , 240 cd / m ² , 350 cd / m ² , 460 cd / m ² , 570 cd / m ² , 680 cd / m ² , and 790 cd / m ^2. , And an equipotential line showing the distribution of each viewing angle of 900 cd / m ² .

In the liquid crystal display device 10 of the present embodiment, the voltage applied to the liquid crystal cell 21 of the viewing angle control panel 2 is switched in at least two stages of the applied voltage V _H or the applied voltage _VL , thereby displaying the display of the liquid crystal display device 10. The state can be switched between a wide viewing angle and a narrow viewing angle.

  By the way, from the viewpoint of privacy protection and security improvement, in recent years, the luminance obtained in the narrow viewing angle mode in the viewing angle control panel not provided with the retardation plate as shown in FIGS. 2 (a) and 2 (b) described above. In the distribution, the narrow viewing angle characteristic is insufficient, and there is an increasing demand for expanding the shielding region in the narrow viewing angle mode.

  Therefore, as shown in FIG. 1, the viewing angle control panel 2 according to the present embodiment includes two retardation plates (an upper retardation plate 24 and a lower retardation plate 25), a liquid crystal cell 21 and a polarizing plate (upper polarization plate). Between the plate 22 and the lower polarizing plate 23). Note that the present invention is not necessarily limited to such a configuration, and there is a phase difference between at least one of the control panel upper polarizing plate 22 and the liquid crystal cell 21 and between the control panel lower polarizing plate 23 and the liquid crystal cell 21. The board should just be provided.

  Here, an optical effect obtained by providing a retardation plate between the polarizing plate and the liquid crystal layer of the viewing angle control panel will be described with reference to FIG. FIG. 7 is a schematic diagram showing a configuration of a viewing angle control panel 2 'provided with one retardation plate.

As shown in FIG. 7, the viewing angle control panel 2 ′ further includes a retardation plate 24 a between the translucent substrate 21 a of the liquid crystal cell 21 and the control panel upper polarizing plate 22. When a narrow viewing angle is obtained by applying a voltage _VL to the liquid crystal cell 21, viewing is performed from a viewing angle other than the azimuth angle of 180 ° shown in FIG. 3 (eg, azimuth angle of 0 °, 90 °, 270 °) If linearly polarized light after passing through the exit control panel under the polarizing plate 23 from the backlight 3, the refractive index of the liquid crystal molecules 21c _{(n e,} n _o) by, birefringence occurs in the liquid crystal layer of the liquid crystal cell 21 It becomes elliptically polarized light. Thereby, the component which permeate | transmits the polarizing plate 22 on a control panel arises, and it becomes a cause of light leakage. The phase difference plate 24a is provided for optically compensating the elliptically polarized light. That is, a retardation plate that generates elliptically polarized light that cancels elliptically polarized light generated in the liquid crystal layer of the liquid crystal cell 21 at a narrow viewing angle is used as the retardation plate 24a. As shown in FIG. 7, the three-dimensional refractive index axes N _X , N _Y , and _NZ of the phase difference plate 24a are defined. That, _{N X} is a component perpendicular to the polarizing transmission axis _{X 22} of the control panel upper polarizing plate 22, _{N Y} is a component parallel to the polarizing transmission axis _{X 22} of the control panel upper polarizing plate 22, _{N Z} is a control panel This component is parallel to the normal line of the upper polarizing plate 22.

8 (a) is a refractive index ellipsoid of the liquid crystal molecules 21c of the liquid crystal cell _21, a _n e> n _o. FIG. 8B shows a refractive index ellipsoid of the phase difference plate 24a, where N _X > N _Z > N _Y. FIG. 8C shows a comparative example, which is a refractive index ellipsoid of a retardation plate (negative A plate film) conventionally used for wide viewing angle of a liquid crystal display device. N _X = N _Z > N _Y.

9A shows the polarization transmission axes X ₂₂ , X of the control panel upper polarizing plate 22 and the control panel lower polarizing plate 23 when viewed from the vicinity of the viewpoint P ₂ (azimuth angle θ = 90 °) shown in FIG. ₂₃ is a schematic diagram showing a relationship between the refractive index ellipsoid F _{21 of} the liquid crystal molecules 21c and the refractive index ellipsoid F ₄ of the phase difference plate 24a. Figure 9 (a), _n e of the refractive index ellipsoid _{F 21} of the liquid crystal molecules 21c, the _{n o,} and the component _{n X22} parallel to the polarizing transmission axis _{X 22} of the control panel upper polarizing plate 22, the control panel under the polarizer It is shown decomposed into a component parallel _{n X23} polarization transmission axis _{X 23} of 23. Further, N _X and N _Y of the refractive index ellipsoid F ₄ of the phase difference plate 24 a are changed from the component N _X22 parallel to the polarization transmission axis X ₂₂ of the control panel upper polarizing plate 22 and the polarization transmission of the control panel lower polarizing plate 23. It is shown decomposed into a component _{N X23} parallel to the axis _{X 23.} As can be seen from FIG. 9A, n _X22 and N _X22 are approximately equal in size, and n _X23 and N _X23 are approximately equal in size. Therefore, the phase difference generated in the liquid crystal layer of the liquid crystal cell 21 is offset by the retardation plate 24a with respect to the viewing angle near the viewpoint P ₂ (azimuth angle θ = 90 °) shown in FIG. 3, and light leakage is prevented. it can. Even when viewed from a viewing angle near azimuth angle θ = 270 °, light leakage is prevented by the same principle as described above.

FIG. 9B shows the polarization transmission axis X ₂₂ of the control panel upper polarizing plate 22 and the control panel lower polarizing plate 23 when viewed from the vicinity of the viewpoint P ₁ (azimuth angle θ = 0 °) shown in FIG. , X ₂₃ , the refractive index ellipsoid F _{21 of} the liquid crystal molecules 21 c, and the refractive index ellipsoid F ₄ of the phase difference plate 24 a. As shown in FIG. 9B, when viewed from a viewing angle near the azimuth angle θ = 0 °, there is almost no phase difference and no light leakage occurs.

  By providing the retardation plate between the polarizing plate and the liquid crystal layer, the narrow viewing angle characteristics in the narrow viewing angle mode can be improved.

  Furthermore, in the viewing angle control panel 2 of the present invention, the retardation value Re1 of the white display portion in the wide viewing angle mode that is the first viewing angle is nλ / 2−λ / 4 <Re1 <nλ / 2 + λ / 4. The retardation value Re2 of the light passing through the viewing angle control panel at the white display portion in the narrow viewing angle mode as the second viewing angle is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4, and the narrow viewing angle mode The retardation value Re3 of the light passing through the viewing angle control panel in the black display portion at n becomes nλ−λ / 4 <Re3 <nλ + λ / 4. Note that n is an integer of 1 or more (n = 1, 2, 3,...), And each n in Re1, Re2, and Re3 may be the same or different.

  In the present embodiment, the retardation plates 24 and 25 are set so that the retardation values as described above are obtained. Here, the “white display portion” means a portion where light can be transmitted and the display can be visually recognized, and the “black display portion” means a portion where light is shielded and the display cannot be visually recognized. To do. Here, the retardation value means a phase shift between each component of light that has passed through the phase difference plate. Here, the light passing through the viewing angle control panel means light having a wavelength of 380 to 780 μm (visible light region) among the light passing through the viewing angle control panel.

  In order to obtain better narrow viewing angle characteristics, the retardation values Re1, Re2, and Re3 are set to nλ / 2−λ / 8 <Re1 <nλ / 2 + λ / 8 and nλ / 2−λ / 8 <, respectively. It is preferable that Re2 <nλ / 2 + λ / 8 and nλ−λ / 8 <Re3 <nλ + λ / 8, where Re1 is an integral multiple of λ / 2, Re2 is an integral multiple of λ / 2, and Re3 is λ More preferably, it is set so as to be as close as possible to an integer multiple of. It is further preferable that Re1 = nλ / 2, Re2 = nλ / 2, and Re3 = nλ. Here, all n are integers of 1 or more, and each n in Re1, Re2, and Re3 may be the same or different.

  In the present invention, it is preferable to use a combination of a plurality of retardation plates having different refractive indexes. According to this, the viewing angle control panel which has the above retardation values can be comprised using the existing phase difference plate.

  In the present embodiment, the configuration shown in FIG. 10 will be described in detail as an example of the configuration of the retardation plate that satisfies the above conditions. FIG. 10 shows a more detailed configuration of the viewing angle control panel 2 provided in the liquid crystal display device 10.

  The viewing angle control panel 2 in the present embodiment has a configuration in which a control panel lower polarizing plate 23, a lower retardation plate 25, a liquid crystal cell 21, an upper retardation plate 24, and a control panel upper polarizing plate 22 are laminated in this order. Yes. Further, as shown in FIG. 10, each of the phase difference plates (upper phase difference plate 24 and lower phase difference plate 25) is, as the upper phase difference plate 24 and lower phase difference plate 25, negative C plates 33a and 33b and λ / 4 plates 32a and 32b. NEZ (trade name; see Non-Patent Document 1) 31a and 31b (biaxial retardation plates), and from the side adjacent to the liquid crystal cell 21 (liquid crystal layer), negative C plates 33a and 33b, λ / 4 plate 32a · 32b, NEZ 31a · 31b has a structure arranged in this order.

  Here, each phase difference plate constituting the phase difference plates 24 and 25 will be described. In describing the characteristics of each retardation plate, each retardation plate has a thickness d as shown in FIG. 11A, and three main refractive indexes nx in the x, y, and z axis directions orthogonal to each other. , Ny, nz.

  11 (b) shows the refractive index ellipsoid of NEZ 31a / 31b, FIG. 11 (c) shows the refractive index ellipsoid of λ / 4 plates 32a / 32b, and FIG. 11 (d) shows the negative C plate. (Negative C) The refractive index ellipsoid of 33a * 33b is shown. NEZ is a biaxial retardation plate having a relationship of nx> nz> ny and (nx−nz) /|nx−ny|=0.1. The λ / 4 plate is such that nx> nz> ny and the in-plane retardation value given by | nx−ny | · d is λ / 4 [nm] (380 nm <λ <780 nm). is there. The negative C plate has a relationship of nx = ny> nz, and the retardation value given by | nx−nz | · d is generally 90 nm to 240 nm.

  Further, although not used for the upper retardation plate 24 and the lower retardation plate 25 according to this embodiment, other examples of the retardation plate that can be used in the present invention include a TAC film and a positive A plate. The TAC film has a relationship of nx = ny> nz, and generally has a retardation value given by | nx−nz | · d of 50 nm to 60 nm. The positive A plate has a relationship of nx> ny = nz. Furthermore, as another phase difference plate, what is described in the nonpatent literature 1 is mentioned, for example.

  In the present invention, the retardation plates used for constituting the retardation plate are particularly limited as long as the retardation values Re1, Re2, Re3 as described above can be obtained by combining a plurality of retardation plates. However, it is possible to use various conventionally known retardation plates.

Further, the arrangement direction of each retardation plate used in the viewing angle control panel 2 shown in FIG. 10 will be described. The NEZ 31a and the negative C33a of the upper retardation plate 24 and the negative C33b of the lower retardation plate 25 are positions where the x-axis is an azimuth angle θ = 135 ° (see FIG. 12) (the polarization transmission axis X of the upper polarizing plate 22 of the control panel). _In a direction orthogonal to the direction ₂₂ ). The λ / 4 plate 32a of the upper phase difference plate 24 and the λ / 4 plate 32b of the lower phase difference plate 25 are both arranged at positions where the x-axis becomes an azimuth angle θ = 180 ° (see FIG. 12). NEZ31b of lower phase difference plate 25, the x axis is disposed in the azimuth angle theta = 225 ° (see FIG. 12) and a position (same direction as the polarizing transmission axis _{X 22} of the control panel upper polarizing plate 22).

  Next, the retardation value (Re value) of the wavelength detected at each viewpoint in the narrow viewing angle mode in the liquid crystal display device 10 including the viewing angle control panel 2 having the configuration shown in FIG. 10 will be described.

First, the viewpoints P _{1 to} P _{5 with} respect to the viewing angle control panel 2 will be described with reference to FIG. As shown in FIG. 12, the azimuth angle θ is a rotation angle of a line connecting a leg of a perpendicular line dropped from a viewpoint to a plane including the surface of the control panel upper polarizing plate 22 and a center 22 c of the control panel upper polarizing plate 22. It is. In FIG. 12, the azimuth angle θ increases clockwise when viewed from the upper side in the normal direction of the polarizing plate 22 on the control panel, with the azimuth angle in the direction of the viewpoint P ₁ (first viewpoint) being 0 °. And In FIG. 12, the azimuth angle θ ₂ of the viewpoint P ₂ (second viewpoint) is 90 °, the azimuth angle θ ₃ of the viewpoint P ₃ (third viewpoint) is 180 °, and the viewpoint P ₄ (fourth viewpoint). The azimuth angle θ ₄ is 270 °. The polar angle Φ is an angle that a straight line connecting the center 22c of the polarizing plate 22 on the control panel and the viewpoint forms a normal to the polarizing plate 22 on the control panel. Here, Φ _{1 to} Φ ₄ are all 45 °. To do. The viewpoint P ₅ (fifth viewpoint) is a viewpoint from the upper side in the normal direction of the control panel upper polarizing plate 22.

FIG. 13A shows a luminance distribution at a narrow viewing angle of the liquid crystal display device provided with the viewing angle control panel shown in FIG. Incidentally, in FIG. _{13 (a), L 1 ~L} 8 are ^{luminance, 50cd / m 2, 100cd /} m 2, 150cd / m 2, 200cd / m 2, 250cd / m 2, 300cd / m 2, 350cd ² is an equipotential line showing the distribution of viewing angles of / m ² and 400 cd / m ² . Further, FIG. 13A shows an angle that matches the azimuth angle shown in FIG.

At the viewpoints P ₁ and P ₅ , the Re value is a value close to λ / 2 (that is, λ / 2−λ / 4 to λ / 2 + λ / 4). In this case, the viewpoints P ₁ and P ₅ are “white display portions” where the display can be visually recognized, as shown in FIG. Further, at the viewpoints P ₂ , P ₃ , and P ₄ , the Re value is a value close to λ (that is, λ−λ / 4 to λ + λ / 4). In this case, the viewpoints P ₂ , P ₃ , and P ₄ are “black display portions” where the display cannot be visually recognized, as shown in FIG.

  On the other hand, in the wide viewing angle mode, the liquid crystal molecules are arranged substantially vertically by applying a voltage of 5.00 V, and almost no retardation occurs in the liquid crystal cell 21. Therefore, in the wide viewing angle mode, the viewing angle control panel 2 having the configuration shown in FIG. 10 includes only the upper retardation plate 24 and the lower retardation plate 25, and the light that has passed through the viewing angle control panel 2 has a Re value in the entire field of view. Is set to be close to λ / 2.

FIG. 13B shows a luminance distribution at a wide viewing angle of the liquid crystal display device provided with the viewing angle control panel shown in FIG. In FIG. 13B, L _{1 to} L ₈ have luminance of 130 cd / m ² , 240 cd / m ² , 350 cd / m ² , 460 cd / m ² , 570 cd / m ² , 680 cd / m ² , and 790 cd. / ^{m 2,} and a equipotential lines showing distribution of each viewing angle of 900 cd / ^{m 2.} FIG. 13B shows an angle that matches the azimuth angle shown in FIG.

As shown in FIG. 13B, it can be seen that the entire field of view (that is, all of the viewpoints P _{1 to} P ₅ ) has appropriate luminance, and the display is visible at each viewpoint.

  The retardation value as described above can be set by deciding a region to be shielded and a region to be visually recognized at a narrow viewing angle and simulating an optimal combination of a liquid crystal layer, a retardation plate, and a polarizing plate. .

  When the luminance distribution as shown in FIGS. 13A and 13B is obtained, the liquid crystal layer has a thickness d of 6.75 μm, and the type of liquid crystal is MS991032 (birefringence Δn Is 0.0615). Further, the applied voltage in this case is 2.95 V in the narrow viewing angle mode and 5.00 V in the wide viewing angle mode.

  The thickness and birefringence of the liquid crystal layer in the liquid crystal display device described here are examples of the present invention, and the present invention is not limited to the above. As the liquid crystal layer used in the viewing angle control panel of the present invention, those generally used as a liquid crystal layer used for viewing angle control can be used. However, in order to obtain the preferable retardation value as described above, it is preferable that the birefringence Δn of the liquid crystal layer is 0.08 or less and the layer thickness d is 5 μm or more and 7 μm or less. According to this, the retardation value difference between the narrow viewing angle mode and the wide viewing angle mode can be set to λ / 2 or more. Therefore, optical compensation with an existing retardation plate is facilitated, and the retardation value as described above can be easily set by combining a plurality of existing retardation plates.

  The configuration of the retardation plates 24 and 25 described here is an example of the present invention, and the present invention is not necessarily limited thereto. 14A to 14C show other examples of the viewing angle control panel of the liquid crystal display device of the present invention. Even when these viewing angle control panels are used, it is possible to obtain viewing angle characteristics in which the viewable range is more limited in the narrow viewing angle mode.

  In the viewing angle control panel 2a shown in FIG. 14A, a TAC film 34a is provided between the control panel upper polarizing plate 22 and the NEZ 31a, and between the control panel lower polarizing plate 23 and the NEZ 31b. The point where the TAC film 34 b is provided is different from the configuration of the viewing angle control panel 2. The viewing angle control panel 2b shown in FIG. 14B includes a negative C plate 33a (or 33b) and a λ / 4 plate 32a (from the side where the upper retardation plate 24 and the lower retardation plate 25 are adjacent to the liquid crystal cell 21). Or the point which has the structure which has arrange | positioned 32b) in this order differs from the structure of the viewing angle control panel 2. FIG. In the viewing angle control panel 2c shown in FIG. 14C, the upper retardation plate 24 and the lower retardation plate 25 are arranged on the side adjacent to the liquid crystal cell 21 from the λ / 4 plate 32a (or 32b) and NEZ 31a (or 31b). Are different from the configuration of the viewing angle control panel 2 in that they have structures arranged in this order.

  As described above, in order to have the viewing angle characteristic having the luminance distribution as shown in FIG. 13A in the narrow viewing angle mode, the retardation plate is a group consisting of NEZ, λ / 4 plate, and negative C plate. In addition, it is preferable that at least a λ / 4 plate and a negative C plate are included as a retardation plate.

In each of the above configuration examples, a retardation plate (an upper retardation plate 24 and a lower retardation plate) is disposed between the liquid crystal layer 21 and two polarizing plates (the upper polarizing plate 22 on the control panel and the lower polarizing plate 23 on the control panel). Although the plates 25) are provided respectively, the present invention is not necessarily limited to such a configuration. However, in the narrow viewing angle mode, a state in which a sufficient shielding effect can be obtained at the viewpoints P ₂ , P ₃ , and P ₄ shown in FIG. 12 (for example, a luminance distribution as shown in FIG. 13A). State) is preferably provided between the liquid crystal layer and the two polarizing plates, respectively.

  As shown in FIG. 1, the above-described liquid crystal display device 10 includes a viewing angle control panel 2 provided on the lower side of the display liquid crystal panel 1, but the present invention is not necessarily limited thereto. Instead, the stacking order of the display liquid crystal panel 1 and the viewing angle control panel 2 may be reversed. That is, for example, as shown in FIG. 15, a liquid crystal display device 10a in which the display liquid crystal panel 1 is stacked on the backlight 3 and the viewing angle control panel 2 is further stacked thereon may be used. Is possible. In this case, the display liquid crystal panel 1 may be a transflective liquid crystal panel.

  Further, the liquid crystal layer of the viewing angle control panel described in this embodiment uses a homogeneously aligned positive nematic liquid crystal, but the present invention is not necessarily limited to this, and a negative nematic liquid crystal may be used. Good. When negative nematic liquid crystal is used, the behavior of liquid crystal molecules is different from that of positive nematic liquid crystal. When no voltage is applied, the liquid crystal molecules are perpendicular to the substrate, and the liquid crystal molecules are parallel to the substrate according to the applied voltage. Inclined in the direction. Therefore, a voltage may be applied to the liquid crystal cell of the viewing angle control panel at a wide viewing angle, and a predetermined voltage may be applied at a narrow viewing angle.

  Further, the present invention can be implemented in various other forms without departing from the main features described above. Therefore, the above-mentioned embodiment is only a mere illustration in all points, and should not be interpreted limitedly. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications, changes and processes belonging to the equivalent scope of the claims are within the scope of the present invention.

Industrial applicability

  The present invention can be applied to a liquid crystal display device including a backlight, a display panel, and a viewing angle control panel for controlling the viewing angle of the display panel. If the liquid crystal display device of the present invention is used, the shielding effect at a narrow viewing angle can be increased, so that the liquid crystal display device can be applied to a display device considering privacy protection and security enhancement.

Claims (10)

A backlight, a liquid crystal display panel, and a viewing angle of the liquid crystal display panel are set between a first viewing angle and a second viewing angle that is within the first viewing angle and is narrower than the first viewing angle. In a liquid crystal display device equipped with a viewing angle control panel that is switched with
The viewing angle control panel is configured by stacking a first polarizing plate, a liquid crystal layer, and a second polarizing plate in this order,
A plurality of retardation plates are stacked between at least one of the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer. The refractive indexes of the laminated retardation plates are different from each other,
The retardation plate has a negative C plate, a λ / 4 plate, and three main refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other, and nx>nz> ny. And a biaxial retardation plate having a relationship of (nx−nz) /|nx−ny|=0.1,
At least one of the first polarizing plate and the liquid crystal layer and at least one of the second polarizing plate and the liquid crystal layer has a negative C plate, λ / 4, from the side adjacent to the liquid crystal layer. Plate, the biaxial retardation plate is laminated in this order,
The retardation value Re1 of the white display portion when the viewing angle of the liquid crystal display panel is the first viewing angle is nλ / 2−λ / 4 <Re1 <nλ / 2 + λ / 4 (n is an integer of 1 or more). And
When the viewing angle of the liquid crystal display panel is the second viewing angle, the retardation value Re2 of the white display portion is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4 (n is an integer of 1 or more). Yes,
The retardation value Re3 of the black display portion when the viewing angle of the liquid crystal display panel is the second viewing angle is nλ−λ / 4 <Re3 <nλ + λ / 4 (n is an integer of 1 or more). A liquid crystal display device.   The retardation value Re1 is nλ / 2 (n is an integer of 1 or more), the retardation value Re2 is nλ / 2 (n is an integer of 1 or more), and the retardation value Re3 is nλ (n is an integer of 1 or more). The liquid crystal display device according to claim 1, wherein the liquid crystal display device is provided. The angle formed by the straight line connecting the center of the surface of the viewing angle control panel and the viewpoint to the normal line at the center of the surface of the viewing angle control panel is the polar angle Φ, and an arbitrary viewpoint that satisfies Φ = 45 ° is the first. And the azimuth angle θ is the rotation angle from the line connecting the leg of the perpendicular line from the first viewpoint to the plane including the surface of the viewing angle control panel and the center of the surface of the viewing angle control panel. In addition,
The viewpoint with θ = 90 ° and Φ = 45 ° is the second viewpoint, the viewpoint with θ = 180 ° and Φ = 45 ° is the third viewpoint, and the viewpoint with θ = 270 ° and Φ = 45 ° is the fourth viewpoint. If the viewpoint from Φ = 0 ° direction is the fifth viewpoint,
At the second viewing angle, the retardation values at the first viewpoint and the fifth viewpoint are nλ / 2−λ / 4 to nλ / 2 + λ / 4 (n is an integer of 1 or more), and a second viewpoint, the third viewpoint, and or claim 1 retardation value in the fourth viewpoint (the n 1 or more integer) nλ-λ / 4~nλ + λ / 4 , characterized in that the 2. A liquid crystal display device according to 2. The retardation plate between the first polarizing plate and the liquid crystal layer, and, according to claim 1, characterized in that between the second polarizing plate and the liquid crystal layer, are provided The liquid crystal display device according to any one of? 5. The liquid crystal according to claim 1 , wherein the polarization transmission axes of the first polarizing plate and the second polarizing plate constituting the viewing angle control panel are orthogonal to each other. Display device. Arranged on at least one of the back and front of the display device for displaying an image, the display device has a first viewing angle and a first viewing angle that is within the first viewing angle and is narrower than the first viewing angle. A viewing angle control panel that switches between two viewing angles,
The first polarizing plate, the liquid crystal layer, and the second polarizing plate are stacked in this order,
A plurality of retardation plates are stacked between at least one of the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer. The refractive indexes of the laminated retardation plates are different from each other,
The retardation plate has a negative C plate, a λ / 4 plate, and three main refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other, and nx>nz> ny. And a biaxial retardation plate having a relationship of (nx−nz) /|nx−ny|=0.1,
At least one of the first polarizing plate and the liquid crystal layer and at least one of the second polarizing plate and the liquid crystal layer has a negative C plate, λ / 4, from the side adjacent to the liquid crystal layer. Plate, the biaxial retardation plate is laminated in this order,
The retardation value Re1 of the white display portion when the viewing angle of the display device is the first viewing angle is nλ / 2−λ / 4 <Re1 <nλ / 2 + λ / 4 (n is an integer of 1 or more). Yes,
The retardation value Re2 of the white display portion when the viewing angle of the display device is the second viewing angle is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4 (n is an integer of 1 or more). ,
The retardation value Re3 of the black display portion when the viewing angle of the display device is the second viewing angle is nλ−λ / 4 <Re3 <nλ + λ / 4 (n is an integer of 1 or more). Viewing angle control panel. The retardation value Re1 is nλ / 2 (n is an integer of 1 or more), the retardation value Re2 is nλ / 2 (n is an integer of 1 or more), and the retardation value Re3 is nλ (n is an integer of 1 or more). The viewing angle control panel according to claim 6 , wherein the viewing angle control panel is provided. The angle formed by the straight line connecting the center of the surface of the viewing angle control panel and the viewpoint to the normal line at the center of the surface of the viewing angle control panel is the polar angle Φ, and an arbitrary viewpoint that satisfies Φ = 45 ° is the first. And the azimuth angle θ is the rotation angle from the line connecting the leg of the perpendicular line from the first viewpoint to the plane including the surface of the viewing angle control panel and the center of the surface of the viewing angle control panel. In addition,
The viewpoint with θ = 90 ° and Φ = 45 ° is the second viewpoint, the viewpoint with θ = 180 ° and Φ = 45 ° is the third viewpoint, and the viewpoint with θ = 270 ° and Φ = 45 ° is the fourth viewpoint. If the viewpoint from Φ = 0 ° direction is the fifth viewpoint,
At the second viewing angle, the retardation values at the first viewpoint and the fifth viewpoint are nλ / 2−λ / 4 to nλ / 2 + λ / 4 (n is an integer of 1 or more), and The retardation values at the second viewpoint, the third viewpoint, and the fourth viewpoint are nλ−λ / 4 to nλ + λ / 4 (n is an integer of 1 or more), or 8. A viewing angle control panel according to 7 . 7. The retardation plate is provided between the first polarizing plate and the liquid crystal layer and between the second polarizing plate and the liquid crystal layer, respectively. The viewing angle control panel of any one of -8. The viewing angle control panel according to any one of claims 6 to 9, wherein the polarization transmission axes of the first polarizing plate and the second polarizing plate are orthogonal to each other.

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